1. Field of the Invention
The present disclosure relates to a circuit breaker having a safety switching part, and particularly, to a circuit breaker having a safety switching part capable of preventing opening of a secondary side terminal of a current transformer when a protecting relay is separated from a main body of the circuit breaker, thus preventing damage to the current transformer and an electric shock accident in advance.
2. Background of the Invention
In general, in a circuit breaker, two current transformers are installed in a main circuit of each phase, and one of the two current transformers is used for measuring a current and the other is used to provide power to a protecting relay connected to the circuit breaker.
In general, a current transformer is a transformer used to widen a measurement range of an alternating current (AC) ammeter by obtaining a small current in proportion to a large AC current from the large AC current.
As for a structure of a current transformer, a primary coil having a small number of windings wound around a laminated iron core and a secondary coil having a large number of windings wound around the laminated iron core, like a transformer. A measurement devices such as an ammeter, a wattmeter, a relay, and the like, are connected to the secondary coil.
FIG. 1 is a perspective view illustrating a configuration in which a main body part of a related art circuit breaker and a protecting relay are coupled, and FIG. 2 is a circuit diagram illustrating connections among main circuit units of the related art circuit breaker main body unit, current transformers, and a protecting relay.
Referring to FIG. 1, in general, a first connector 11 is installed on one side of a main body unit 10 of a circuit breaker which interrupts a fault current.
Also, a second connector 21 connected to the first connector 11 is installed on one side of the protecting relay 20.
Referring to FIG. 2, a main circuit unit 12 is provided in each phase of the circuit breaker main body unit 10, and two current transformers are installed for each phase.
A measurement current transformer 31 is used to measure a current flowing in the main circuit unit 12, and a power supply current transformer 32 is used for supplying power.
A secondary side terminal 32b of the power supply current transformer 32 used for supplying power is connected to a power source unit 23 of the protecting relay 20.
Also, a secondary side terminal of the measurement current transformer 31 is connected to a measurement unit 22 of the protecting relay 20.
In the aforementioned connection scheme, the first and second connectors 11 and 21 are connected to form a conduction state.
In a state in which the circuit breaker main body unit 10 and the protecting relay 20 are coupled, when the protective relay 20 is physically separated from the circuit breaker main body unit 10 for maintenance, the first and second connectors 11 and 21 are also separated from each other.
Thus, the secondary side terminal of the measurement current transformer 31 is separated from the signal measurement unit 22, and the secondary side terminal 32b of the power supply current transformer 32 is separated from the power source unit 23.
Accordingly, the secondary side terminals of the current transformers 31 and 32 are open.
Here, as for characteristics of a current transformer, a rated value of a primary current of the transformer may be various ranging from tens of ampere (A) to thousands of amperes (A), but a rated value of a secondary current is 5 A in most cases, and a current ratio between primary and secondary coils is in inverse proportion to each of the number of windings of the primary and secondary coils.
As for the secondary side terminal of the current transformer, it is safe to short the secondary side terminal, but it is very dangerous to open the secondary side terminal.
This is because, when the secondary coil or terminal is opened in a state in which a current flows in the primary coil, a primary side current acts to magnetize the entire iron core to cause the iron core to be saturated to heat, causing a high possibility of damage to the coil, explosion of the current transformer, or an electric shock accident.
Here, the measurement current transformer 31 used for the purpose of measurement forms a current lower than that of the power supply current transformer, so it may be safe.
Meanwhile, in the case of the power supply current transformer 32, since it is used for supplying power, a current thereof is formed to be higher than that of the measurement current transformer 31.
Thus, when the secondary side terminal 32b of the power supply current transformer 32 is opened, a high voltage is generated to damage the secondary side terminal 32b to damage the current transformer and cause an accident such as an electric shock accident, or the like.
In FIG. 2, reference numeral 32a denotes a primary side coil.
A related art document may be Korean Laid Open Publication No. 10-2004-0039556 (Publication date: May 12, 2004).